The present invention relates generally to the measurement of fluid opacity, and in particular to measuring the turbidity of a fluid in which micro-organisms are growing, for the purpose of monitoring the growth of these organisms.
Still more specifically, the invention relates to a method of carrying out such measurements and to an apparatus for carrying the method into effect.
When micro-organisms are grown in a vessel, for example a so-called "fermentor", their development must be monitored from time to time. This is done by testing the turbidity of the liquid nutrient medium in which they are being grown. The measurements can be taken within the vessel itself or a sample can be removed from the vessel to an exterior measuring chamber. In the latter case it is of course necessary to provide pumps which withdraw the sample and return it subsequently to the vessel, and pumps, the conduits and the separate measuring chamber must be frequently and separately sterilized, i.e. they must be sterilized independently of any sterilization that may be carried out in the vessel at the end of the production of a batch of micro-organisms.
In all prior-art devices the measuring results have not been as accurate as is desirable. The reason for this is that the micro-organisms require for proper growth constant admission of gaseous fluid, such as air or oxygen, into the liquid nutrient medium. This means that the gaseous fluid is present in form of bubbles in the liquid nutrient medium, and when a turbidity measurement is carried out, the presence of these bubbles in the sample of the nutrient medium to be measured tends to adversely affect the accuracy of the measurement. While the problem has been recognized, heretofore no way has been suggested for eliminating gas bubbles from the sample before the measurement is carried out, because the liquid nutrient media and the microorganisms contained therein do not readily lend themselves to a de-gasification prior to carrying out the measurements.